Research Indicates That The Womb Can Be A Very Noisy Place For Baby

August 6, 1989|By Rick Mcguire, Health & Fitness News Service

Investigators at the University of Southern California couldn't believe their ears when they began eavesdropping on pregnant women and their babies. Using specially designed microphones, they found that babies within the womb live in an almost totally unfiltered world of sound.

''I couldn't believe what noise a baby is subjected to,'' said Jeffrey Phelan, M.D., an associate professor of obstetrics and gynecology at the USC School of Medicine.

In fact, while listening to the precise audio levels heard by a baby, Phelan admitted, ''I had to turn down the monitor because my ears couldn't stand the noise level.

''It's amazing to me,'' said Phelan, ''and it's certainly not something we had anticipated. We thought it would be quiet.''

The investigation began in 1981 with a simple study to see if a baby is influenced by external noise. After nearly two years of weekly experiments, Phelan and his associates had carefully documented that fetal heart rate and activity levels did respond to external sounds such as pure tones and music.

Although little research exists on the effects of noise on the fetus, a few clues are offered by the little data that are available.

''There seems to be no disagreement that noise does reach the fetal inner ear, and changes in fetal heart patterns and fetal movements suggest that anxiety and discomfort may be experienced by the fetus exposed to 100 decibels or more,'' reported the Journal of Occupational Medicine.

A decibel (dB) is the basic unit of sound measurement. A whisper produces 20 dB, an ordinary conversation 60 dB, and an express train 100 dB. Sounds become annoying at about 70 dB (a vacuum cleaner) and potentially damaging at 85 or 90 dB (a motorcycle). Ear pain is associated with sounds of 100 dB or more.

Although the data to date hint at deleterious effects from fairly high levels of sound, Phelan suspects some adverse fetal effects might occur at much lower noise levels. For example, considering the suspected fetal sleep/wake cycle of 20 to 30 minutes, Phelan wonders what effect noise could have on the fetus's ability to rest.

The earliest fetal response to sound appears to be at about 26 weeks, according to Phelan, and we know that by 32 weeks the fetal ear is fully developed.

Fortunately, one developmental factor could protect tiny fetal ears from loud noise. According to Yvonne Sininger, Ph.D., of the House Ear Institute in Los Angeles, the fetal middle ear is fluid-filled, not air-filled as in an adult. Thanks to this amniotic fluid surrounding the fetus, baby's hearing sensitivity could automatically be dropped by 15 to 20 decibels.

But, Sininger said, if Phelan's findings are confirmed, ''There could be some major implications to this news. Baby could obviously be at risk from external noise.''

And, she wonders, how could noise get through all of mother's tissue and amniotic fluid with such little loss of sound?

Phelan isn't sure yet, although he does note, ''Sound is amplified in a liquid medium.'' So, while the amniotic fluid might help muffle sounds once inside baby's ear, the same fluid might actually help amplify sound as it's carried to Baby.